Theologian John Piper has called the 21-year prison sentence for Anders Breivik "outrageous."

"He was deemed sane and sentenced to serve 21 years in prison 'in a three-cell suite of rooms equipped with exercise equipment, a television and a laptop.' That's 100 days of posh prison time for each person he murdered, with a legal release possible at age 53," he wrote in a blog post Monday.

"Life is cheap in Norway."

Breivik, 33, was sentenced on Friday by an Oslo court, which declared him sane, for murdering 77 people last July. He was convicted of terrorism and premeditated murder after he confessed to bombing an Oslo building and shooting dozens of people at the Norwegian Labor Party's annual summer camp at Utoya island.

In court, the Norwegian gunman apologized to "militant nationalists" for not having killed more people. He has argued that he wanted to stop the "Islamization" of Norway.

Under Norwegian law, the maximum sentence allowed is 21 years but the court ruled that he can be locked up for as long as he's considered a threat to society.

The sentencing has sparked debate about Norway's justice system, with some calling it too soft. The death penalty was abolished in 1979.

Piper pointed to C. S. Lewis' essay in 1949 titled "The Humanitarian Theory of Punishment," where the Christian author explained that "treating criminals not with a view to punishment, but only with a view to remediation and deterrence is the end of justice and the seedbed of tyranny," as Piper paraphrased.

"He (Lewis) explains that the moment you disconnect punishment from what a person deserves, you disconnect it from justice; because 'the concept of Desert is the only connecting link between punishment and justice," Piper stated.

In Lewis' words: "Thus when we cease to consider what the criminal deserves and consider only what will cure him or deter others, we have tacitly removed him from the sphere of justice altogether; instead of a person, a subject of rights, we now have a mere object, a patient, a 'case.'"

Commenting on the court's ruling to keep Breivik in prison as long as he is considered dangerous, Piper said, "The issue is not what he deserves. The issue is not justice. The issue is power in the hands of judges who will decide if he has been 'rehabilitated' sufficiently, and if his detainment has served the community to a suitable degree.

"This is the seedbed of tyranny. To be sure, there is a place for rehabilitation and deterrence. But only under the humanizing sway of justice."

Without the right punishment or justice, then mercy can't exist, the theologian argued.

"The Christian – the biblical – concept of mercy toward wrongdoers only exists in relation to justice. Showing mercy, in relation to wrongdoing, means treating someone better than they deserve," he stated. "If the concept of ill-desert, and with it the concept of justice, is lost, mercy ceases to be. It is replaced by sentiment and caprice.

"As Lewis observes, 'The essential act of mercy was to pardon; and pardon in its very essence involves the recognition of guilt and ill-desert in the recipient.'"